The invention relates to a procedure for cooling electromagnetic actuating devices for internal combustion engine valves in which some of a fluid circulating in the internal combustion engine, particularly lubricating oil, is passed through each electromagnetic actuating device (i.e., an actuator).
An electromagnetic valve actuator for an internal combustion engine has immense advantages because of the freedom with respect to the valve control times, i.e., with respect to the pertinent opening and closing points of the valve. However, relatively high forces must be applied for actuation, especially for opening the valve, which necessitates a certain minimum coil and armature size. As a result, it is extremely difficult to accommodate a conventional actuator housing in a modern cylinder head of an internal combustion engine that, for example, drives a motor vehicle. Additionally, when the valves are actuated, a relatively large amount of heat develops in the coils, especially at higher actuation frequencies, which has to be dissipated in a suitable way.
Pure convection cooling of the actuator housing in the surrounding air is insufficient for this purpose, especially when the constricted space conditions just described are taken into account.
German Patent No. 197 14 496 A1 discloses a conventional electromagnetic valve actuator that is fluid cooled. In particular, a cooling channel is provided in an actuator housing through which some of the stream of fluid circulating inside the internal combustion engine is passed as a cooling fluid. This cooling fluid stream may be provided by engine coolant fluid (e.g., the liquid coolant of a liquid-cooled internal combustion engine) or may be derived from the lubricating oil stream of the internal combustion engine. Alternatively, as disclosed in U.S. Pat. No. 3,882,833, the cooling fluid stream may also be passed directly through the actuator, as opposed to passing through cooling channels integrated in an actuator housing.
A percentage of the power developed by the internal combustion engine is lost to circulating the cooling fluid to the actuators, a plurality of which are normally present in an internal combustion engine. This percentage is generally greater when the lubricating oil circulating in the internal combustion engine is used as the cooling fluid, and especially when the lubricating oil is cold and has a higher viscosity, i.e., before the internal combustion engine has warmed-up. It is desirable to keep power losses due to cooling fluid circulation as low as possible in order to minimize fuel consumption of the internal combustion engine.